The specific objective of this project is to study natural animal cancer occurrence to gleen any information that would be of use in understanding human cancer. The studies take the form of (1) characterization of animal cancers such as incidence rates, including age-, sex-, and breed-specific, (2) etiological studies such as seeking factors or variables that may be affecting the risk or occurrence of various cancers in animals and relating them to human cancer occurence, (3) human-animal association studies as to whether there is increased human cancer in households where an animal with cancer has lived, and (4) human-animal comparisons such as age- and sex-specific incidence rate patterns for clues to possible environmental effects modifying patterns. BIBLIOGRAPHIC REFERENCES: Schneider, R. and Vaida, M.L.: Survey of Canine and Feline Populations: Alameda and Contra Costa Counties, 1970. J. Am. Vet. Med. Assn. 166: 481-486, 1975. Schneider, R.: Observations on Overpopulation of Dogs and Cats. J. Am. Vet. Med. Assn. l67: 281-284, 1975.